Recently much attention has been focused on the problem of reducing pollution of the atmosphere, especially in and around large metropolitan areas. A great deal of effort has been expended on reducing pollutants emitted by factories, industrial installations and even homes. It has also been recognized that the emissions of internal combustion engines have been major sources of pollution, particularly in the form of unburned hydrocarbons, carbon monoxide and other noxious gases. The automotive industry has embarked on a large-scale program to reduce the noxious gases emitted by passenger cars and trucks. A number of different solutions to the problem have been explored and several different ones have been adopted at least in part.
One so called "third generation," solution to the problem involves the use of catalytic converters in an exhaust pipe to convert noxious gases to safer gases. There are basically two main types of such converters presently contemplated. An oxidizing catalytic conveter speeds up and completes the burning of hydrocarbons and carbon monoxide. A reducing catalytic converter removes oxygen from oxides of nitrogen. An oxidizing catalytic converter needs additional oxygen to function properly and this can be provided by an engine-driven air pump. The air pump forces air into an exhaust pipe of the engine immediately upstream of the oxidizing catalytic converter.
However, it is desirable to provide a control valve for controlling the flow of forced air to the exhaust pipe to avoid certain problems. One such problem arises because additional burning of gases in an oxidizing catalytic converter creates additional heat. If the increased heat becomes great enough there could be physical damage to the converter. Of course at lower speeds, and lower engine loads, such as is normally encountered in city driving, the heat level is quite moderate. Under heavier load conditions and higher speeds, such as is encountered in steady cruising at highway conditions, the heat can be, and normally is, much greater.
Still another problem area may arise during deceleration of a vehicle where injected air creates a violent type of burning in an exhaust system which, in some instances, results in audible afterfire. This is an objectionable noise and may create prssures that could be harmful to an exhaust system.
Yet another problem area arises during periods of high engine acceleration when so much fuel is in exhaust gases that injected air causes too large a "fire". Such a fire may damage a catalytic converter. Thus, a valve for controlling flow from an air pump to an exhaust pipe immediately upstream of an oxidizing catalytic converter should, ideally, cut off air flow during periods of high acceleration and high deceleration, and should reduce air flow during periods of high speeds. It is an object of this invention to provide such a valve assembly.